Electrical transmission line

ABSTRACT

A rotary joint for an RF transmission line includes a flexible plastic disc member having a smooth annular surface adjacent its inner periphery, structure for clamping the outer periphery of the disc to one section of the transmission line and a surface of elastomeric material softer than the annular surface of the disc member secured to the other section. The inner peripheral surface of the disc is urged, by gas pressure in the line and/or a biasing structure, against the surface of elastomeric material. This structure provides a gastight seal so that a gaseous dielectric may be maintained under pressure within the transmission line.

United States Patent Inventor Donald Sewell 2,438,457 3/1948 Schlosser 277 9 X Raymond, Maine 2,750,215 6/1956 Bermingham 277/65 [21] Appl. No. 814,969 Re. 24,940 2/1961 Stephens 277/89 X [2 PM d zp :2 :33? 3,359,871 12/1967 Kamman 277/88 x Patente 0v. [73] Assignee Sola Basic Industries, Inc. FOREIGN },)ATENTS Mflwaukefi, Wis 958,639 5/1964 Great Brltam 277/82 Primary ExaminerRichard E. Moore Al!0rneyWillis M. Ertman [54] ELECTRICAL TRANSMISSION LllNlE 4 (Ilaims, 3 Drawing Figs. I I

ABSTRACT: A rotary 01nt for an RF transmission l1ne 1n- [52] v.5. C11 339/8, dudes a flexible plastic disc member having a smuoth annular 277/'277/88339/1 surface adjacent its inner periphery, structure for clamping [51] Int. Cl H0111 39/02 the outer periphery of the disc to one Section f m trunsmis [50] Field of Search 339/8, 5, 5km "He and a surface f elasmmeric muterim ft than the 277/88' 89 annular surface of the disc member secured to the other section. The inner peripheral surface of the disc is urged, by gas [56] References Cited pressure in the line and/or a biasing structure, against the sur- UNITED STATES PATENTS face of elastomeric material. This structure provides a gastight 2,407,445 9/1946 Phillips 339/8X seal so that a gaseous dielectric may be maintained under Re. 22,920 9/1947 Bruno 339/8 X pressure within the transmission line.

y 61 so wmr /ww/ ELECTRICAL TRANSMISSION LINE SUMMARY OF INVENTION This invention relates generally to electrical transmission lines and more particularly to rotary-joint seals of particular advantage in coaxial lines for the transmission of RF electrical energy.

In certain types of coaxial transmission lines the dielectric between the inner and outer conductors is a gas, such as dry air, maintained at a superatmospheric pressure, e.g. l pounds per square inch gauge. Where one portion of the line must rotate relative to another portion, as in a rotary antenna feed, a rotary seal compatible with the electrical, mechanical and environmental requirements is required to prevent leakage of the dielectric gas to the atmosphere. The seal must prevent contaminants, such as dust, from entering the system, while minimizing RF noise introduced due to differential movement of the transmission line components, In addition, the seal must maintain its frictional and sealing quality and otherwise operate satisfactorily over the relatively wide ranges of atmospheric conditions and temperatures to which such transmission lines may be subjected. Further, such transmission line structure should be long-lived to avoid the time and expense of shutdowns caused by maintenance or replacement thereof.

An object of the invention is to provide a novel and improved rotary electrical transmission line seal particularly adapted for use in pressurized coaxial lines which effectively seals the line from the atmosphere over wide ranges of pressures and temperatures.

Another object of the invention is to provide a novel and improved rotary electrical transmission line seal which incorporates nonmetallic seal elements and does not introduce electrical distortions into the transmission line system.

Still another object of the invention is to provide a rotary electrical transmission line seal which is simple, inexpensive, reliable, and long-lived, requires no lubrication and whose sealing ability is enhanced by its use.

A still further object of the invention is to provide a rotary electrical transmission line seal of low frictional characteristics and especially adaptable for use at low temperatures, e. g. 65 F.

The invention features a rotary joint for an RF transmission line having two tubular conductor sections, the first of the sections being arranged to rotate relative to the second of the sections. The joint includes a seal structure having a flexible plastic disc member with a smooth annular surface adjacent its inner periphery; structure for clamping the outer periphery of the disc member so that the disc member is fixed to one of said conductor sections; and a surface of elastomeric material that is softer than the annular surface of the disc member secured to the other conductor section. The inner periphery of the disc member is flexed to engage the elastomeric material to provide a gastight seal so that a gaseous dielectric under pressure may be maintained within the transmission line. In particular embodiments, the disc member is a fluorocarbon polymer preferably polytetrafluoroethylene; and the elastomeric material has a durometer hardness in the range of 40-80, and. preferably is a silicone rubber that has a durometer hardness in the order of 70.

In a preferred embodiment a support structure, fixed on the first conductor section, supports a bearing structure that in turn supports the second conductor section. O-rings are arranged to form effective seals in the radial direction between the support structure and the atmosphere. An annular polytetrafluoroethylene barrier washer has its outer periphery secured to the bearing structure and its inner periphery extends radially inward from the bearing structure. A sleeve is secured to the second conductor section and has at least one O-ring arranged to effectively fomi a seal between the sleeve and the second conductor section. The sleeve has a circular groove in its end wall, and a silicone rubber O-ring is pressed into the groove. A biasing structure urges the barrier inner periphery of the barrier disc against the silicone rubber O-ring to form an effective seal.

In a particular embodiment the biasing structure includes an annular follower member and a sine wave washer, the washer being mounted on the bearing structure and the follower member being mounted on the washer and acting against the inner periphery of the plastic seal disc. The follower member and the washer cooperate to apply a uniform force against the inner periphery of the seal disc and urge that inner periphery against the elastomeric surface of the silicone rubber O-ring. The structure further includes a flexible annular wiper strip arranged to effectively seal the joint seal from atmospheric contaminants.

Other objects, features, and advantages will appear from the following description of a preferred embodiment of the invention. As other embodiments of the invention will be apparent to those skilled in the art, it will be understood that this description is illustrative of only one embodiment of the invention. In the attached drawings:

FIG. 1 is a perspective view of a portion of a coaxial electrical transmission line, the upper section of which is rotatable relative to the lower section, constructed in accordance with the invention;

FIG. 2 is a sectional view of the transmission line structure taken along line 2-2 of FIG. 1; and

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1 showing the seal structure in greater detail.

DESCRIPTION OF PARTICULAR EMBODIMENT There is shown in FIG. 1 a portion of a 3%inch coaxial transmission line, generally designated 10, comprising outer conductor 12 and inner conductor M, respectively, having upper conductor section 12a and 14a arranged to rotate relative to their respective lower conductor sections llZb and Mb at a predetermined speed (e.g., 5 r.p.m.) A tubular support structure 16 is disposed over the lower end of the upper conductor sections and includes a lower flange structure 18 and an upper flange structure 20.

As shown in FIG. 2 tubular inner conductor sections lla and 14b are disposed within outer conductor sections 12a and 11212 and are secured to and supported in coaxial relation therewith by dielectric disc members 13 (FIG. 3). The space between conductors l2 and M is filled with a suitable dielectric gas, e.g., dry air, at a superatmospheric pressure, e.g., l5 p.s.i.g.

The support structure 16 is secured to lower conductor section 12b and the upper conductor section Illa is arranged to rotate relative to that structure. Each flange structure includes two flange members, the upper structure including members 22 and 50 and the lower structure including members 23 and 24. The two annular flanges of each flange structure M, 20 are bolted together and radially sealed by O-rings 48, 46, respectively. The inner races of bearings 26, 28, are mounted on sleeve 30 that is secured by set screws 31 to the lower end of upper conductor section 12a. The outer bearing races are secured in tubular support cylinder 33 which extends between the two flange members 22 and 24.

The inner periphery 34 of flange member 23 of lower flange unit 18 is seated on the upper end of conductor section 12b and is spaced from the lower end of conductor section 12a to define annular gap 36. A compensating sleeve 38 provides the electrical path length at the operating frequency necessary to transmit power across gap 36.

Flange 50 has a series of eight holes which receive clamping bolts 51, a series of eight tapped holes 53 at a first stepped surface 68 in its upper surface, an annular groove 66 in second stepped surface 70 and a third stepped surface 72 adjacent its inner periphery; an annular groove 54 in its lower surface which receives O-ring $6 and a recess 55 which extends in wardly from the outer race of bearing 26. A beryllium-copper spring washer, 0.010 inch thick and 4.38 inches in diameter before forming, is distorted to form sine waves in eight places to an amplitude ofO. l 30 inch to provide a spring washer and is mounted on surface 72. A ring follower 88 is supported by spring washer 86. This follower has a cylindrical wall 89 and a radial wall, the upper surface 90 of which has a horizontal flat surface 0.12 inch in width, an outer peripheral surface inclined at an angle of 15 from the horizontal and an inner peripheral surface inclined at an angle of from the horizontal. Above follower 88 is a flexible seal disc member 78 in the form of a polytetrafluoroethylene (Teflon l) washer which has an outer diameter of 5.25 inch, an inner diameter of 3.5 inch, and a thickness of 0.062 inch, the inner periphery of the washer being recessed in a facing operation to remove imperfections to a maximum depth of 0.005 inch for a distance of V4 inch back from its inner periphery. This disc 78 is clamped by clamp block 80 which is secured in place by bolts 81 which cooperate with threaded holes 53 and is sealed against O-ring 94 disposed in groove 66. In this position, as indicated in FIG. 3, the slip washer 78 is flexed upwardly at its inner periphery by spring washer 86 and supporting follower 88 The second component of the rotary joint secured to the upper outer conductor section 120 and includes a sealing sleeve 61; a second sleeve 57 which overlies the sealing sleeve 61; a spacer ring 65; a clamp ring 67; and two O-rings 62, 64, the lower O-ring 64 being secured between shoulder 63 of sleeve 57 and the lower surface of sleeve 61 and the upper O- ring being secured between the upper end of sleeve 61 and spacer ring 65. This assembly is secured together by bolts 69 which pass through clamp ring 67 so that the two O-rings 62, 64 are compressed. Set screws 60 secure the assembly to conductor section 120. At the lower end of sleeve 57 is a groove 56, 0.185 inch in width, in which is disposed an 0.210 inch diameter silicone rubber O-ring 84 AMS-3357A specification). An 0.042 inch diameter vent hole 71 is provided at the base of groove 56. At intermediate shoulder 73 there is an annular slot 75 of V4 inch depth and 0.10 inch width in which is disposed a felt wiper 92. The upper joint assembly is positioned on upper conductor section 12a so that O-ring 84 engages the faced surface of seal washer 78 and felt wiper 92 engages the upper surface of clamp member 80.

In operation, annular space is filled with a suitable gas, e.g. dry air, at a superatmospheric pressure, for example 15 I p.s.i.g. The gas passes through gap 36 and exerts a force on follower 88 and seal washer 78, supplementing the biasing force of spring washer 86 and urging washer 78 against silicone rubber O-ring 84. O-ring 84 is firmly secured in groove 56 and rotates relative to and on top of washer 78. O-rings 62 and 64 prevent the gas from passing along the surface of conductor 12a. Wiper 92 prevents foreign matter from entering the area of the joint from the atmosphere. At zero and very low pressures sine wave washer 86 and follower 88 urge the inner periphery of washer 78 upward and assure seal contact which contact is augmented by gas pressure.

The faced surface of seal washer 78 becomes smoother with use. In addition, it retains its flexibility and low frictional quality at very low temperatures, for example 70 F. and at these low temperatures the seal requires no additional rotational torque as is required with conventional seals of a radial configuration. The effect of the high expansion and contraction characteristics of polytetrafluoroethylene is minimized by selecting the thickness of the static seal portion to obtain a tolerable percentage change in thickness as a function of temperature. The contour of the internal configuration of this seal may be varied to change the sealing pressure inherent at the face seal. The cooperating elastomeric seal surface 84 retains its flexibility over a wide range of temperatures and does not flake, crumble or wear when subjected to these seal contact pressures.

The rotary joint seal constructed in accordance with the invention provides excellent seals at very low temperatures, and operates over a wide temperature range (-65 F. to +1 26 F. Pressurized seals of the invention has been operated at temperatures down to -70 F. with essentially no increase in rotational torque. In a 3%inch line, this joint has a starting torque of less than 45 inch-pounds maximum throughout the operatmg temperature range and operates reliably at substantially higher rotational speeds than the normal operating rotational speed of 5 r.p.m. Thus the invention provides an efficient, reliable seal structure for a rotary joint in an electrical transmission line which does not require lubrication and which has long life and operates reliably over a wide range of temperatures. As the disc member is harder than the elastomeric member no defined track is worn in the disc member and therefore the joint structure can absorb a considerable amount of misalignment without adversely effecting its sealing ability.

While a particular embodiment of the invention has been shown and described, modifications thereof will be apparent to those skilled in the art and therefore is not intended that the invention be limited to the disclosed embodiment nor to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. A rotary joint for an RF transmission line, said transmission line having two coaxially aligned tubular conductor sections, the first of said conductor sections being arranged to rotate relative to the second of said conductor sections, comprising a support structure fixed on said first conductor section,

a bearing structure mounted between said support structure and said second conductor section,

an annular fluorocarbon polymer barrier member having an outer periphery secured to said support structure and an inner periphery extending radially inward from said support structure,

a sleeve secured to said second conductor section, said sleeve having an end wall, and an annular groove in said end wall,

an O-ring of elastomeric material softer than said fluorocarbon barrier member secured in said groove, said elastomeric material having a durometer hardness in the range of 40 80, and

biasing structure arranged to urge the inner periphery of said barrier member against said O-ring to form an effective seal, said biasing structure comprising an annular member and a sine wave washer, said washer being mounted on said bearing structure and said annular member being mounted on said washer and below the inner periphery of said barrier, said annular member and said washer being arranged to cooperate to apply a uniform force against said barrier member inner periphery and to urge said barrier inner periphery against said O-ring to form an effective seal.

2. Apparatus according to claim 1 wherein said support structure further comprises O-rings arranged to efiectively seal said support structure radially.

3. Apparatus according to claim 2 and further including an annular strip of flexible material, said strip being arranged to effectively seal said O-ring and said barrier inner periphery from said contaminants in the atmosphere.

4. Apparatus according to claim 3 wherein said barrier member is manufactured of polytetrafluoroethylene and said O-ring is manufactured of silicone rubber. 

1. A rotary joint for an RF transmission line, said transmission line having two coaxially aligned tubular conductor sections, the first of said conductor sections being arranged to rotate relative to the second of said conductor sections, comprising a support structure fixed on said first conductor section, a bearing structure mounted between said support structure and said second conductor section, an annular fluorocarbon polymer barrier member having an outer periphery secured to said support structure and an inner periphery extending radially inward from said support structure, a sleeve secured to said second conductor section, said sleeve having an end wall, and an annular groove in said end wall, an O-ring of elastomeric material softer than said fluorocarbon barrier member secured in said groove, said elastomeriC material having a durometer hardness in the range of 40 -80, and biasing structure arranged to urge the inner periphery of said barrier member against said O-ring to form an effective seal, said biasing structure comprising an annular member and a sine wave washer, said washer being mounted on said bearing structure and said annular member being mounted on said washer and below the inner periphery of said barrier, said annular member and said washer being arranged to cooperate to apply a uniform force against said barrier member inner periphery and to urge said barrier inner periphery against said O-ring to form an effective seal.
 2. Apparatus according to claim 1 wherein said support structure further comprises O-rings arranged to effectively seal said support structure radially.
 3. Apparatus according to claim 2 and further including an annular strip of flexible material, said strip being arranged to effectively seal said O-ring and said barrier inner periphery from said contaminants in the atmosphere.
 4. Apparatus according to claim 3 wherein said barrier member is manufactured of polytetrafluoroethylene and said O-ring is manufactured of silicone rubber. 